Hemispiroalkaplanes: Hydrocarbon cage systems with a pyramidal-tetracoordinate carbon atom and remarkable basicity

A new class of saturated hydrocarbons in which a spiropentane-type unit is bound by a cyclic hydrocarbon, has been investigated by using ab initio mol ecular orbital calculations at the B3-LYP and MP2 levels. These molecules h ave been given the trivial name hemispiroalkaplanes. Hemialkaplanes. which are analogous molecules built-up from a neopentane-type unit and a cyclic h ydrocarbon, have also been examined. The hemispiroalkaplanes are predicted to contain a pyramidal-telra-coordinate carbon atom that possesses a lone p air of electrons. Protonation at this apical carbon atom is found to be hig hly favourable, resulting in a remarkably high basicity for a saturated hyd rocarbon. The proton affinities of the hemispiroalkaplanes are calculated t o be more than 1170 kJ mol(-1), even great er than that of the diamine ''pr oton sponges". Structural parameters, heats of formation and strain energie s for the novel hydrocarbons are detailed.